1. Field
The present invention relates to an image forming apparatus such as a copier, a printer, and a facsimile machine, and a failure detection method of detecting a failure in such an image forming apparatus.
2. Background Art
As a background color image forming apparatus, a tandem-type image forming apparatus for forming a color image is known which includes a plurality of toner image forming devices disposed along an intermediate transfer belt which constitutes an image carrying member for carrying thereon toner images of a plurality of colors. Each of the toner image forming devices includes a photoconductor, which constitutes an image carrying member for carrying thereon a toner image of a single color, and a charging device, a development device, a cleaning device, and so forth, which surround the photoconductor.
In the tandem-type image forming apparatus, the toner image forming device gradually deteriorates in function and lapses into an abnormal state due to such factors as frictional wear accompanying normal operation, external infiltration of harmful material such as paper powder, increase in adhesion of toner and loss of an external additive due to excessive mixing of the toner caused by an unexpected operation and so forth, contamination and degradation of the cleaning device or the charging device, and random failure of the cleaning device or the charging device.
In the abnormal state of the toner image forming device, image quality is degraded. Specifically, an undesirable abnormal image having a longitudinal streak extending along the rotational direction of the photoconductor, a blurred image, an abnormal image having a lateral streak extending perpendicular to the rotational direction, a blotted image having spots, a whited-out image, and so forth are generated. Normally, however, the toner image forming device continues to be operated, with such controls as image density control and color shift control performed to change an image forming condition and suppress the above-described deterioration of the image quality. Then, when such controls as the image density control and the color shift control are no longer capable of suppressing the deterioration of the image quality and an abnormal image is formed on a sheet, a user notices the abnormality of the toner image forming device, and performs a repair operation such as replacement of the toner image forming device.
As described above, in the background image forming apparatus, the repair is requested when the abnormal image is formed on the sheet. A normal image forming operation cannot be performed until the repair is completed. Thus, the image forming function is suspended. As a result, a substantial loss of time is caused to a user of the apparatus.
A variety of image forming apparatuses have been known that predict or determine a failure of the toner image forming device. For example, according to one background technique, an image forming apparatus detects the electric potential of an electrostatic latent image formed on the photoconductor of the toner image forming device by using a surface electrometer, and determines the replacement timing of the toner image forming device on the basis of the result of the detection.
According to another background technique, an image forming apparatus forms a linear toner image in an area on the photoconductor excluding a sheet-feeding area, collects the toner of the toner image, and determines the replacement timing of the toner image forming device on the basis of the amount of collected toner.
According to still another background technique, an image forming apparatus predicts the life of the toner image forming device on the basis of the number of times the toner image forming device is used. Further, according to still yet another background technique, an image forming apparatus outputs a signal prompting the replacement of the toner image forming device when any one of the layer thickness of the photoconductor, the remaining toner amount, and a gap between the photoconductor and a development roller falls below certain predetermined values.